The present invention is directed to a method of controlling the condensation of sulfur trioxide in flue gases to thereby inhibit the corrosion of metallic parts because of the sulfuric acid inherently formed. Basically, the requirements on the addition of particulate alumina (Al2O3) to the flue gas at a place where it is experiencing turbulence, and where its temperature is below 1000* F, and preferably within the range of 450* F. to 650* F.